Dominant wavelength

The definitions of dominant wavelength d, complementary dominant wavelength c and excitation purity Pe are given on this and the following page. These are also known as the Helmholtz coordinates.

Any colour, when plotted on the CIE diagram may be specified in terms of its' dominant wavelength, which is the wavelength of the spectrum locus where the line drawn from the chromaticity point of the illuminant, through the chromaticity point of the colour and then extended, intersects the locus.

Dominant wavelength is generally abbreviated to d.

The dominant wavelength of a colour in the purple triangle of the chromaticity diagram bounded by the illuminant point, 400nm and 700nm on the spectrum locus is specified as the complementary of the greenish colour found on the spectrum locus by extending the line joining the illuminant point to the sample colour backwards to the top of the CIE diagram. it is abbreviated to c.